Radio equipment is widely used in respective fields of control, monitoring and so forth of consumer electrical appliances including cell phones. Then, in the radio equipment, an antenna miniaturization of which is possible while maintaining high radiation efficiency is required.
As the antenna which has been widely used conventionally, there exists the slot antenna. This slot antenna is the one which has been made so as form a slot of λ/2 in length and 0.01λ in width in a metal substrate in a case where a wavelength has been denoted by λ and to electrically connect an edge of the slot with a coaxial line.
On the other hand, a technology of feeding electric power to the slot by electromagnetic coupling by using the stripline, not directly feeding the electric power to the slot by electric connection is proposed in Non-Patent Literature 1. In addition, a proposal is made in regard to a configuration for facilitating establishment of matching with 50Ω power feeding and heightening a coupling rate and then heightening (not lowering) the radiation efficiency in the slot antenna.
FIG. 14 are the ones showing the antenna based on Non-Patent Literature 1.
As shown in FIG. 14, a slot 2 of about λ/2 (λ is the wavelength) in length is formed in the center of a metal substrate 1 of 100 mm×100 mm in length and breadth, and a stripline 4 is arranged in a direction intersecting with a longitudinal direction of the slot 2 with a dielectric 3 of 0.4 mm in thickness being interposed.
It is designed as the antenna of a frequency f of a slot antenna, where f=2.4 GHz band. Accordingly, it is formed such that a slot length is 54 mm and a slot width is 1.2 mm.
On the other hand, the stripline 4 projects from the slot 2 by λg/4 in length at a leading end 5 (the upper side) thereof as shown by an arrow Q in order to heighten the radiation efficiency by heightening an amount of coupling (a state of impedance matching) with the 50Ω power feeding. Λg denotes a propagation wavelength of the frequency at which resonance just occurs on the stripline 4 when the slot length is a.
In addition, the stripline 4 is arranged at a position which has been offset from the center in a length direction of the slot 2 to the left side by 20 mm in order to facilitate establishment of the impedance matching.
A not shown high frequency circuit is connected to the other end (the lower side) of the stripline 4.
According to this slot antenna, it is possible to easily produce an antenna section having the slot and a power feeding section by photoetching and so forth in comparison with a case of direct power feeding via a coaxial line.
However, in the slot antenna described in Non-Patent Literature 1, it is necessary to project (a part marked with the arrow Q) the stripline 4 from the slot 2 by λg/4 in length.
Accordingly, there was such a problem that the size of the antenna becomes large.